The present invention relates generally to analytical test devices and, more particulaly to a method and device for measuring blood gas parameters, preferably pH, pCO2, and pO2, in a blood sample, where the blood sample of a patient is fed into at least one measuring cell of an analyzer.
In the blood gas multi-analyzers described in the literature and commercially available the measuring cells are thermo-stabilized at body temperature, i.e., at 37.0° C. Besides measuring the blood gas parameters pH, pCO2 and pO2, these analyzers are used to measure electrolytes, metabolic parameters and Hb-derivatives. For this reason the maximum operating temperature of such analyzers should always be somewhat lower than the temperature of the measuring cell and lies between 31° C. and 33° C. in commercially available devices.
In U.S. Pat. No. 4,548,259 A a measuring cell is described in the context of a chemical analyzer for photometric measurement of a liquid sample, which is thermostabilized by being provided on opposing walls with thermoelements, e.g., Peltier elements, the side walls of the measuring cell furthermore being provided with temperature sensors for measuring the cell temperature. After a sample has been fed into the measuring cell, the cell may be heated or cooled by means of the Peltier elements—depending on the output signal of the temperature sensors—until a predetermined working temperature in the range of 37° C.±0.2° C. is attained. The device described is suitable for the photometric measurement of blood samples, for instance, during which temperature must be kept constant.
From DE 26 51 356 A1 a measuring device for the photometry of liquid samples is known, in which a Peltier element is proposed as a heat-source or heat-sink for the thermo-stabilization of small measuring vessels (and thus small measurement samples). This permits rapid and highly accurate adjustment of the working temperature (preferably 30° C.) of the measuring device.
Finally, a blood gas analyzer is described in U.S. Pat. No. 4,717,548, which determines blood gas parameters, such as pH, pCO2, pO2 and temperature, in an extracorporeal blood flow situation, for instance during open-heart surgery, and which records the individual signals in real time. The signals are used for parameter monitoring and may activate alarm and switching functions when preset values are exceeded.
If conventional blood gas multi-analyzers are used for blood gas analysis with patients whose body temperature deviates from the normal temperature (37° C.), for instance in special surgery cases during which body temperature is artificially lowered, it is standard practice to correct the values for pH, pCO2 and pO2 obtained from the measuring device with the use of mathematical models, in order to find the medically relevant values at the actual body temperature of the patient. Such corrections are rather imprecise, however, and errors of up to 50% may occur.